Construction method for root-type foundation anchorage and bored, root-type cast in-situ pile with anchor bolts

ABSTRACT

The invention discloses a construction method for rooted foundation anchorage, comprising the following steps:
         precasting a concrete caisson in sections, excavate or bore hole for the caisson sinking, reserving holes for projection of anchor roots in the wall of caisson;   cleaning the bottom of the bore hole, and sealing the bottom with concrete; precasting the beam type concrete roots and, within the bore hole, projecting the roots into the earth around the caisson;   sealing a concrete cover over the bore hole to form a flat cap, which can be used as the cap of a bridge foundation.       

     The invention also discloses a construction method for a root-type cast in-situ bored pile with anchor roots, comprising the following steps:
         placing a reinforcement cage in a bored hole; each guide framework is internally provided with anchor roots;   using a vibration extruder to squeeze the roots in the reinforcement cage;   using the squeezing head of the vibration extruder to squeeze the anchor roots from top to bottom gradually. The invention greatly improves the traditional foundation structure. The anchor roots increases friction and structural stability greatly, thus making it possible to reduce gravity of the structure.

FIELD OF THE INVENTION

The invention relates to a foundation construction method for civil engineering, bridge construction and hydraulic structure, in particular to a construction method for root type caisson foundation.

BACKGROUND OF THE INVENTION

At present, foundations in common use in engineering construction at home and abroad comprising: pile foundation, cylinder pile foundation, open caisson foundation and underground diaphragm wall foundation.

The pile foundation refers to a foundation composed of a group of piles jacked or sunk into the soil and a cap connecting the pile top. External force is distributed on various pile heads via the cap, and then transmitted into surrounding soil and deep soil below the pile toe via the pile shaft and the pile toe. The pile foundation, suitable for deep soil, has the advantages of the lightest structure, higher degree of mechanization of construction and faster construction progress among all deep foundations, being a relatively economical foundation structure. Some bridge foundations bear major horizontal force, for example, bridge pier foundations bear horizontal load from left-right direction, and thus the pile foundations thereof usually adopt bi-directional batter piles; some beam bridge abutments mainly bear unidirectional soil pressure, whose pile foundations usually adopt unidirectional batter piles. Vertical pile foundations, rather than batter piles, are suitable for those piles with large diameter and considerable rigidity, for example, frequently used large-diameter bored piles at present. Frequently used pile foundations at present, including precast pile, common cast-in-place pile, tube-sinking cast-in-situ pile, artificial bored pile and slurry bored pile etc., have different disadvantages in use. For example, hammering the precast pile causes noise pollution, demanding for more reinforcing steel bars, thus leading to higher cost of construction. The common cast-in-place pile has the disadvantages of greater consumption of reinforcing steel bars and cement, intractable disposing of uncompacted soil on the pile toe and possible contraction of the pile shaft. The tube-sinking cast-in-situ pile also has the disadvantages of noise pollution, quality problem of the pile shaft, lower bearing capacity and frequent prone to occur accidents.

The tube caisson foundation refers to a foundation structure composed of reinforced concrete and prestressed concrete or steel pipe concrete column and reinforced concrete cap. The tube caisson foundation also can be composed of a single large-scale tubular column. As a deep foundation, the tube caisson foundation is usually suitable for bridges, whose tubular column is buried into the earth at a certain depth, with the bottom of the tube caisson foundation falling into solid earth or anchored into rocks as far as possible. All load exerted on the reinforced concrete cap (which is on the top of the tube caisson foundation), the bridge pier and upper structure is transmitted by the tubular column to deep dense soil or on rocks. The tubular columns (short precast steel, reinforced concrete or prestressed concrete tube couplings), are lengthened at construction sites, and then projected into the earth by way of vibration or torsional pendulum, in the meantime, mud in the tubular columns are drilled out, dug out or sucked out so as to reduce sinking resistance. In case that tubular columns fall on bed rock, the tube walls thereof can be used as casing pipes for drilling, and then reinforced concrete is poured to anchor the tubular columns to the bed rock so as to improve structural stability and bearing capacity. In addition, large-diameter holes are drilled in stratum, then precast tubular columns are projected into the holes and cement mortar is poured between the column wall and the hole wall so that tubular columns are tightly anchored to the earth in order to increase bearing capacity. The tubular columns can be filled with concrete or reinforced concrete, or even made into a hollow body in part. The tube caisson foundation is only suitable for riverbeds without overburdens or with thick overburdens, unsuitable for regions with geological defects.

The open caisson foundation refers to a deep foundation characterized in that upper load is transmitted to foundation by an open caisson which serves as a foundation structure. The open caisson, a pitshaft bottomless and coverless, consists generally of a cutting shoe, a borehole wall and a partition wall etc. Earth in the open caisson is excavated out and thus the open caisson sinks until reaching a designed elevation, and the open caisson is subject to bottom sealing by concreting, bottom filling and head cover building, in this way, the open caisson foundation is completed. The open caisson foundation, characterized by larger cover depth, good integrity, good stability and larger bearing area, is capable of bearing larger vertical and horizontal load. In addition, the open caisson serves both as a foundation and as a cofferdam in construction, characterized by simple construction technology, safe and reliable technology, dispensed with special professional equipment, available for a compensated foundation, thus avoiding excessive foundation settlement, subject to a wide application in deep foundation or underground structures, for example, bridge pier foundations, underground pump rooms, pools, oil depots, mine vertical shafts, large-scale equipment foundation and high-rise and super high-rise building foundations etc. Serving both as a foundation and as cofferdam in construction, the open caisson is dispensed with pit wall support or pile-plank retaining wall, thus simplifying the construction. However, the open caisson foundation has a longer construction time and is demanding for construction technology; furthermore, the open caisson is prone to incline or sink resulted from quick sand in construction.

The underground diaphragm wall foundation refers to a continuous underground wall with the functions of seepage proofing, earth retaining and load bearing, which is formed by excavating a narrow and deep groove under the ground by using groovers by feat of wall supporting of slurry and pouring with suitable materials. The underground diaphragm wall, characterized by little vibration, low noise, large rigidity and good impermeability, disturbance-free to surrounding foundations, is available to a constituting arbitrary polygon continuous wall with large bearing capacity to replace with pile foundation, open caisson foundation or caisson foundation. With a wide application to soil, the underground diaphragm wall foundation is available for construction in weak alluvium, medium ground, dense gravel bed and rock foundations. Preliminarily used for dam body seepage proofing and reservoir groundwatertrapping, later the underground diaphragm wall foundation is developed into part or whole of retaining walls and underground structures, applicable to deep-seated basement, underground parking garage, underground street, underground railroad, underground warehouse and mine etc. The underground diaphragm wall foundation is difficult for construction under special geological conditions (for example, soft mucky soil, alluvium containing boulder and super-hard rock etc.), and is prone to misalignment of adjacent wall sections and water leakage in case of improper construction method. In addition, compared with other construction methods, the underground diaphragm wall foundation has higher construction cost in case of serving as a temporary retaining structure. Besides, mud disposal is quite troublesome for construction in cities.

SUMMARY OF THE INVENTION

Objective of the invention: in allusion to difficult foundation building, demanding foundation treatment and technical requirements as well as high risks and other technological problems in the foundation construction under the prior art, the invention aims at providing a construction method for root type caisson foundation characterized by simple construction technology, less material consumption, fast construction and safe and reliable construction.

In order to solve the above-mentioned technological problems, the invention discloses a construction method for rooted foundation anchorage, comprising the following steps:

Precasting a concrete caisson in sections, excavate or bore hole for the caisson sinking, reserving holes for projection of anchor roots in the wall of caisson, and sinking the caisson into the earth by its self-weight, which stops sinking when the bottom runs into rocks; the anchor root has a cusp at one end, and a flat head at the other end;

Cleaning the bottom of the bore hole, and sealing the bottom with concrete;

Precasting the beam type concrete roots and, within the bore hole, projecting the roots into the earth around the caisson;

And sealing a concrete cover over the bore hole to form a flat cap, which can be used as the cap of a bridge foundation.

In the invention, more preferably, the precast beam type concrete roots are, within the bore hole, projected in to the earth, comprising the following steps:

The inwall of the caisson is internally provided with a vertical slide rail which is anchored to the caisson by rail anchors;

The inwall of the slide rail is provided with a diagonal bracing, on the same section of which a circular rail beam is arranged;

On the circular rail beam is provided with a pipe jacking platform, on which a steel support rod is arranged;

The anchor root is placed on the a pipe jacking platform with the cusp pointing at the anchor root hole, while the flat head at the other end jacked by a jack until the anchor root is projected into the earth.

In the invention, in the process of jacking the anchor root by the jack, a crane is used to lift the anchor root so as to guarantee the anchor root to be projected into the earth in accordance with the design direction.

In the invention, inside the anchor root hole is provided with a rubber water seal and a rubber water fender successively; the rubber water seal is provided with a crossed open pore in the middle, and the cusp end of the anchor root is successively pushed into the rubber water seal and the rubber water fender. The rubber water fender bends toward outside of the open caisson and tightly wraps the outer wall of the anchor root when the anchor root is jacked in because inside dimension of the rubber water fender is less than external dimension of the pipe-jacking, thus playing a part of hermetic seal.

In the invention, on the outer wall of the anchor root hole on the wall of the open caisson is provided with a steel hole-sealing plate on which a presplitting line is arranged diagonally. A layer medium plate is inserted into the anchor root and the steel hole-sealing plate is sealed up by welding in case a rubber water seal and a rubber water fender are installed.

In the invention, on the outer edge of the anchor root hole is provided with a grouting hole.

The invention also discloses a construction method for a root-type cast in-situ bored pile with anchor roots, comprising the following steps:

A reinforcement cage is placed into a bored hole; the reinforcement cage consists of an external main reinforcement and an internal main reinforcement; a guide framework, which is manufactured by welding a guide ring at both ends by more than two reinforcing steel bars, is welded between the external main reinforcement and the internal main reinforcement; the guide framework is subject to uniform arrangement along a peripheral direction inside the external main reinforcement and the internal main reinforcement; guide frameworks are arranged one line by one line along the axial direction of the external main reinforcement and the internal main reinforcement from top to bottom, and each guide framework has an inclined horizontal plane, convenient for extrusion, vibration and expansion; the main reinforcement is anchored to the internal main reinforcement by stirrups;

Each guide framework is internally provided with an anchor root front end of which is shaped like a cone while the tail end an arc surface;

A vibration extruder is used to squeeze the roots in the reinforcement cage; the vibration extruder comprising a circular table-shaped squeezing head, a connecting rod and a hydrostatic rapping device connected successively;

The squeezing head is used to squeeze the anchor roots from top to bottom gradually, and is pulled out after all anchor roots are in place; pouring concrete into cast-in-situ bored pile, particularly guaranteeing adequate concrete pouring into the guide framework which serves as an anchoring point for the anchor root.

In the construction method mentioned above in the invention, the circular table of the squeezing head is 1-2 times of the distance between two adjacent guide frameworks in height; the upper anchor roots are squeezed by the squeezing head while in the meantime the lower anchor roots stabilize and maintain direction of the squeezing head.

In the construction method mentioned above in the invention, the reinforcement cage is externally provided with a geotextile or a sleeving in advance at those strata prone to hole collapse according to borehole log, so as to guarantee thickness of the protective layer for main reinforcement.

The principle of the invention: the root type caisson foundation refers to a bionic foundation formed by reserving incremental launching holes in the open caisson and pushing precast anchor roots in the earth after the open caisson sinks to the designed elevation until anchor roots are concreted with the open caisson. The root type caisson foundation is capable of improving both horizontal and vertical bearing capacities of bridge foundations, and capable of fully meeting stability requirements of foundations against foundation settlement, slide, uplift and overturn. In term of material rigidity, the root type caisson foundation is a combination of rigid body (open caisson), finite-rigidity beam (anchor root) and elastic plastic body (the earth); wherein, the finite-rigidity beam plays a good role in rigidity transition and stress distribution and transfer. Besides, structural design is available for the cap, the anchor body and the cable saddle of the root type caisson foundation. Global optimization is available by dispersing anchor cable, reducing arm of tension force of inhaul cable and other measures, thus giving full play of soil resistance at the most extent. In addition, the root type caisson foundation, breaking through the stress mechanism in which tradition anchorage foundations purely rely on frictional resistance between bottom of foundation and subbase, gives full play of the foundation beam, simplifies construction of thick overburden layer foundations by way of “breaking up the whole into parts”, and improves prefabricated construction, thus making construction quality controllable.

The invention has beneficial effects as below: greatly optimizing traditional foundation structures, greatly enhancing friction force by adopting anchor roots, increasing structural stability by using bond stress of the earth to anchor roots, and making it possible to reduce structural gravity, thus having better economical efficiency; the root type caisson foundation, simple in construction technology, rapid and safe and reliable in construction, can be not only widely used in hydraulic structures (for example, bridges) for bearing horizontal pull and vertical pressure, but also popularized to large-scale foundations.

BRIEF DESCRIPTION OF THE DRAWINGS

Further detailed description related to the invention is made in conjunction with the accompanying drawings and embodiments so as to make advantages of the invention more clearly:

FIG. 1 is a diagram of a rooted foundation anchorage in construction.

FIG. 2 is a structure diagram of the anchor root hole in the invention.

FIG. 3 is a vertical view of the rooted foundation anchorage in FIG. 1.

FIG. 4 is a diagram for showing the construction in which a rubber water seal and a rubber water fender are successively arranged in the rooted foundation anchorage in FIG. 1.

FIG. 5 is a structure diagram of the rubber water seal in the invention.

FIG. 6 is a diagram for showing the construction method for a root-type cast in-situ bored pile with anchor roots mentioned in the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Just as shown in FIG. 1 and FIG. 3, the invention discloses a construction method for rooted foundation anchorage, comprising the following steps:

Precasting a bore hole 1 in sections, reserving in the wall of the bore hole holes 3 for the projection of anchor roots 2, and sinking the caisson into the earth 4 by its self-weight, which stops sinking when the bottom runs into rocks; the anchor root has a cusp at one end, and a flat head at the other end;

Cleaning the bottom of the bore hole, and sealing the bottom with concrete;

Precasting the beam type concrete roots and, within the bore hole, projecting the roots into the earth around the caisson 4;

And sealing a concrete cover over the bore hole to form a flat cap, which can be used as the cap of a bridge foundation.

The precast beam type concrete roots are, within the bore hole, projected in to the earth, comprising the following steps:

The inwall of the caisson is internally provided with a vertical slide rail 5 which is anchored to the bore hole by rail anchors 6;

The inwall of the slide rail is provided with a diagonal bracing 7, on the same section of which a circular rail beam 8 is arranged;

On the circular rail beam is provided with a pipe jacking platform 9, on which a steel support rod 10 is arranged;

The anchor root is placed on the a pipe jacking platform with the cusp pointing at the anchor root hole, while the flat head at the other end jacked by a jack until the anchor root is projected into the earth.

In the process of jacking the anchor root by the jack, a crane is used to lift the anchor root so as to guarantee the anchor root to be projected into the earth in accordance with the design direction. Just as shown in FIG. 2, a grouting hole 11 is arranged on the outer edge of the anchor root hole 3, in which is the anchor root 2.

Just as shown in FIG. 4 and FIG. 5, inside the anchor root hole is provided with a rubber water seal 12 and a rubber water fender 13 successively; the rubber water seal is provided with a crossed open pore 14 in the middle, and the cusp end of the anchor root is successively pushed into the rubber water seal and the rubber water fender. The processing step is as below: after the open caisson sinks by sucking slurry and is subject to bottom sealing and then water drawing, the rubber water fender plays a role of preventing muddy sand outside of the open caisson from entering inside of the open caisson. After bottom sealing of the open caisson, sweeping residual muddy sand away, keep both the anchor root and the jack in place for pushing. The cutting shoe of the anchor root pierces the rubber water seal; on the point of touching the rubber water fender, the anchor root is tightly wrapped by the rubber water seal, which is compressed at 1 cm at this moment, thus sealing up. Jacked by the jack, the cutting shoe of the anchor root pierces the rubber water fender and pushes forward. When the anchor root is jacked in position, the rubber water seal wrapping the anchor root up is compressed at 2 cm, thus rubber projecting outward is completely compressed in the connecting trough of a steel jacket. Rubber can be compressed by more than 25%, thus rubber sheet with a width not less than 6 cm in the connecting trough can fully meet requirements of compression. The steel jackets in the inner layer and the outer layer are welded with each other after the anchor root is jacked in position.

Just as shown in FIG. 6, a construction method for a root-type cast in-situ bored pile with anchor roots wherein comprising the following steps:

A reinforcement cage is placed into a bored hole; the reinforcement cage consists of an external main reinforcement 15 and an internal main reinforcement 16; in the external main reinforcement 15 and the internal main reinforcement 16 is provided with a pile main reinforcement 17 on which a hoisting reinforcement 18 is arranged; a guide framework 19, which is manufactured by welding a guide ring 21 at both ends by more than two reinforcing steel bars 20, is welded between the external main reinforcement and the internal main reinforcement; the guide framework is subject to uniform arrangement along a peripheral direction inside the external main reinforcement and the internal main reinforcement; guide frameworks are arranged one line by one line along the axial direction of the external main reinforcement and the internal main reinforcement from top to bottom, and each guide framework has an inclined horizontal plane; the main reinforcement is anchored to the internal main reinforcement by stirrups 22; the reinforcement cage is externally provided with a geotextile or a sleeving.

Each guide framework is internally provided with an anchor root 23 front end of which is shaped like a cone while the tail end an arc surface;

A vibration extruder is used to squeeze the roots in the reinforcement cage; the vibration extruder comprising a circular table-shaped squeezing head 24, a connecting rod 25 and a hydrostatic rapping device 26 connected successively;

The squeezing head is used to squeeze the anchor roots from top to bottom gradually, and is pulled out after all anchor roots are in place; pouring concrete into cast-in-situ bored pile, particularly guaranteeing adequate concrete pouring into the guide framework which serves as an anchoring point for the anchor root.

The circular table of the squeezing head is 1-2 times of the distance between two adjacent guide frameworks in height.

The invention provides a thought and method for construction of a root type caisson foundation. There are a plurality of methods and approaches for concrete realization of the technical scheme, and what is mentioned above is just a preferred embodiment. Those of ordinary skill in the art can, under the premise of not against the inventive principle, make some improvements and embellishment, which shall be deemed to be within the scope of protection of the invention. Those unspecified in the embodiment can be achieved by using the prior art. 

1. A construction method for rooted foundation anchorage wherein comprising the following steps: precasting a concrete caisson in sections, excavate or bore hole for the caisson sinking, reserving holes for projection of anchor roots in the wall of caisson, and sinking the caisson into the earth by its self-weight, which stops sinking when the bottom runs into rocks; the anchor root has a cusp at one end, and a flat head at the other end; cleaning the bottom of the bore hole, and sealing the bottom with concrete; precasting the beam type concrete roots and, within the bore hole, projecting the roots into the earth around the caisson; and sealing a concrete cover over the bore hole to form a flat cap, which can be used as the cap of a bridge foundation.
 2. The construction method for rooted foundation anchorage according to claim 1, wherein the precast beam type concrete roots are, within the bore hole, projected in to the earth around the caisson, comprising the following steps: the inwall of the caisson is internally provided with a vertical slide rail which is anchored to the caisson by rail anchors; the inwall of the slide rail is provided with a diagonal bracing, on the same section of which a circular rail beam is arranged; on the circular rail beam is provided with a pipe jacking platform, on which a steel support rod is arranged; the anchor root is placed on the a pipe jacking platform with the cusp pointing at the anchor root hole, while the flat head at the other end jacked by a jack until the anchor root is projected into the earth.
 3. The construction method for rooted foundation anchorage according to claim 2, wherein in the process of jacking the anchor root by the jack, a crane is used to lift the anchor root so as to guarantee the anchor root to be projected into the earth in accordance with the design direction.
 4. The construction method for rooted foundation anchorage according to claim 1, wherein inside the anchor root hole is provided with a rubber water seal and a rubber water fender successively; the rubber water seal is provided with a crossed open pore in the middle, and the cusp end of the anchor root is successively pushed into the rubber water seal and the rubber water fender.
 5. The construction method for rooted foundation anchorage according to claim 1, wherein on the outer edge of the anchor root hole is provided with a grouting hole.
 6. A construction method for a root-type cast in-situ bored pile with anchor roots wherein comprising the following steps: a reinforcement cage is placed into a bored hole; the reinforcement cage consists of an external main reinforcement and an internal main reinforcement; a guide framework, which is manufactured by welding a guide ring at both ends by more than two reinforcing steel bars, is welded between the external main reinforcement and the internal main reinforcement; the guide framework is subject to uniform arrangement along a peripheral direction inside the external main reinforcement and the internal main reinforcement; guide frameworks are arranged one line by one line along the axial direction of the external main reinforcement and the internal main reinforcement from top to bottom, and each guide framework has an inclined horizontal plane; the main reinforcement is anchored to the internal main reinforcement by stirrups; each guide framework is internally provided with an anchor root front end of which is shaped like a cone while the tail end an arc surface; a vibration extruder is used to squeeze the roots in the reinforcement cage; the vibration extruder comprising a circular table-shaped squeezing head, a connecting rod and a hydrostatic rapping device connected successively; the squeezing head is used to squeeze the anchor roots from top to bottom gradually, and is pulled out after all anchor roots are in place; pouring concrete into cast-in-situ bored pile, particularly guaranteeing adequate concrete pouring into the guide framework which serves as an anchoring point for the anchor root.
 7. The construction method for a root-type cast in-situ bored pile with anchor roots according to claim 6, wherein the circular truncated cone of the squeezing head is 1-2 times of the spacing of two adjacent guide frameworks in height.
 8. The construction method for a root-type cast in-situ bored pile with anchor roots according to claim 6, wherein the reinforcement cage is externally provided with a geotextile or a sleeving. 